Microphone



Jan. 26, 1943. J. l.. HATHAwAY MICROPHONE 'Original Filed June 4. 193'? Eff-@WAHM MMO/v6 Patented Jan., 26, i943 stares param i arcaica Mrcaornonr Jarrett L. Hathaway, Manhasset, N. Y., assignor to Radio Corporation of America, a corporation ci' Delaware Original application June 4, 1937, Serial No.

146,405. Divided and this application December 8, 1939, Serial No. 308,239

2 Claims.

Thisinvention relates to a new and novel com-' posite microphone arrangement which involves. the use of two microphones to produce an improved uni-directional pickup.

This application is a, division of my copending application Serial No. 146,405, led June 4, 1937, the claims in this-application being d lrected to the microphone switching circuits.

This application is also somewhat allied to the Anderson Patent #2,173,219, patented Sept. 19, 1939, in which patent there is an arrangement of a multiplicity of pressure gradient responsive ribbons at suitable angles to each other.

' An object of this invention is to provide an electrically combined microphone arrangement in which an improved vuni-directional pickup can be obtained.

Another object. of this invention is the improved switching arrangement whereby it is possible tochange the uni-directional characteristics by one hundred and eighty degrees 180) by merely reversing the output polarity of Out` puts of the pressure gradient responsive ribbons wherein the microphones are directly Yfed to sepeither one of the microphones comprising the Y uni-directional microphone. Also, by the use of suitable'impedance microphones, the switching maybe done at a point which is a long distance from the microphones, or at a point where the sound originates.

A feature of this invention is the combining of a non-directional microphone with a bi-directional microphone to give an improved unidirectional pattern, which may be controlled in pattern shape and sense of direction by the operator.

Another feature of this invention is the novel arrangement of the sound responsive elements in which a non-directive sound responsive element is located in the horizontal plane and the bidirectional sound responsive element is located in a perpendicular plane. y

This invention will best be understood by referring to the. accompanying drawing, in which:

Fig. 1 is a front view of the improved combined microphones;

Fig. 2 is a side view of Fig. 1;

Fig. 3 is a microphone directional patternl plotted irr polar coordinates to show the directional characteristics of this combined microphone: Y

Fig. 4 is a. simple circuit arrangement show ing the method by which the uni-directional.

pattern is changed by one hundred'and eighty degrees (1809) by reversing its output polarity; and

Fig. 5 shows a circuit switching arrangement,

arate pre-amplifiers. Y

Referring now in' detail to Figs. 1 and 2 of the drawing, the non-directional microphone I is mounted on a. bi-directional microphone 4. The

nondirectional microphone consists essentially of asmalldiaphragm 2, an armature, coil, and a permanent magnet 3 supported within a small, spherical casing. The entire structure of this microphone is sc small as to make it non-directional for all frequencies involved. The bi-directional microphone 4 isof the velocity type, and comprises a ribbon 5 which is suspended in position in free space between the poles of a permanent magnet 6. Sound waves reaching the ribbon vibrate it within the vmagnetic eld set up by the magnet. The vibrations of the ribbon being in exact accordance with the sound vibration occurring as it does within the magnetic iield sets up a corresponding alternating current potential which is brought out byl the leads 1. are pivotally mounted on a support 8.

Referring now to the curve shown in Fig. 3 of the drawing, the bi-directional characteristic pattern is indicated in full by lines l0, the nondirectional eld pattern characteristic being shown by the dot and dash line Il and the improved combined uni-directional pattern is indicated by the dash lines l2, and it will be noted that the voltage output of the new and improved uni-directional combination is substantially twice that of either the bi-directional or non-directional microphone in one direction, .and approximately zero in the opposite.

invention is often greaterin that the two microvphones .may be so combined that not only unidirectionaLcharacteristics in one direction but in the opposite direction, as well, may be obtained,

The combined microphones I and 4 A or it may be connected to be used as a bi-directional or non-directional microphone, and these changes of characteristics may be controlled remotely from the microphone location. The output leads I and I4 may be fed to a preamplifier I5, as shown in Fig. 4, through separate faders I1, the leads of the bi-directional microphone 4 being connected to a polarity reversing switch I8 in such a manner that the output polarity may be reversed at will. This arrangement makes it possible to obtain four different patterns without moving the physical position of the stand. For example, the non-directional microphone may be used separately, the bi-directional microphone may be used separately, the non-directional and bi-directional microphones I and 5. respectively, of Fig. 2, may be used in combination to give a pattern facing to the left, as shown in Fig. 3, or its direction may be reversed by reversing the polarity of switch I 8 to give a pattern, not shown, to the right.

While Fig. 4 shows but one of the various electrical means for combining the two microphones, other means may be obtained by feeding the microphones direct to the preamplifiers and from the preampliers combining the outputs through an attenuator I1 and switch I8, as shown by Fig. 5, or, if desired, the non-directional and the l. bi-directional microphones may also be provided with simple resistor networks to obtain the correct; amplitude relationship before entering the preamplifiers.

'I'he mechanical arrangement of the microplanes may be reversed and also other angular relationships of the microphones used, provided, however, that close proximity of each microphone is established. Furthermore, this invention should not be limited to the device shown.

but only by such limitations as are clearly imposed in the appendedclaims What is claimed is:

l. A microphone system comprising two microphones, one of said microphones having a non-directional characteristic and the other microphone having a bi-directional characteristic, two fading resistances, a preamplifier, said microphone having the non-directional characteristie being connected in series with one of said fading resistances, and to the input circuit of said preamplifier, a switch for electrically connecting the microphone having the bi-directional characteristic in parallel with the last-mentioned microphone to the input of said preamplifier and in series with the other fading resistance, and also for reversing the output circuit of at least I one of said microphones to change the overall directional response pattern of said microphones when used together.

2. A microphone circuit comprising two microphones, one of which has a non-directional characteristic and the other of which has a bidirectional characteristic, two fading resistances, a preamplier, a double pole, double throw switch connecting both of said microphones in parallel and to the input circuit of said preamplifier, said microphone having the non-directional characteristic being connected in series with one Aof said fading resistances and the other microphone having the bi-directional characteristic being connected in series with the other fading resistance, the poles of said double pole, double throw switch being arranged and connected to reverse `the direction of the current iiow from the output of at least one of said microphones to the input circuit of said preamplifier to change the direction of response, of the microphones when used together, approximately JARRETT L. HATHAWAY. 

